Supravalvular aortic stenosis (SVAS) was seen in 128 families. In 23 families several members had SVAS. In 4 families the Williams-Beuren Syndrome (WBS) was present whereas members of 8 families had some features of the syndrome in addition to their cardiac lesion. In conclusion, no distinct separation can be made between WBS and SVAS. The genetic pattern is autosomal dominant with variable expressivity. The gene frequency is estimated at 10(-4) and the mutation rate at 2.5 . 10(-5).